Temperature control



Jun 13, 1939.

G. M. PELTZ 2,162,116

TEMPERATURE CONTROL v I Filed Oct. 13, 1953 F 3 Sheets-Sheet 1 F15 1Fig.4

[NV OR 60F? DON M Z y I a A'r'ronwcya June 13, p -rz TEMPERATURE CONTROL3 Sheets-Sheet Filed Oct. 13, 1933 I NVE NTOR N M.

Gomao f /3 2 M mw June 13, 1939. G. M. PELTZ TEMPERATURE CONTROL FiledOct. 15, 1933 3 Sheets-Sheet 3 INVENTOR GORDON M. PELTZ ATTORNEYSPatented June 13, 1939 UNITED STATES PATENT OFFICE TEMPERATURE comor.

Delaware Application October 13, 1933, i l 693,457

16 Claims.

This application is a continuation in part of my application Serial No.567,063 filed October 5,

My invention relates to the control of conditions such as steampressure, temperature and the like. From a more specific aspect also, itrelates particularly to the control of temperature.

Generally speaking, my invention enables one to hold the condition atmore nearly the desired value or values than has been possibleheretofore, at least with relatively simple apparatus of generalapplication.

Thermostatic elements are known, e. g. a bimetallic element, which iscapable of holding a temperature at very close to a desired value,providing the thermostatic element is arranged to activate a suitableheat source immediately the temperature falls below some certain degreeand to more or less deactivate the heat source again immediately thetemperature rises above the same certain degree. ments are so sensitiveto temperature changes and to slight mechanical forces however, thatsimple 25 thermostatic arrangements of this kind un desirable in certainsituations, such as in the con. trol of the heating of living rooms andhomes, since in such systems parts are brought into action with annoyingfrequency.

Heretofore various expedients have adopted to reduce this frequency, poptically all cf which, so far as I am aware, dependent on or involveactivation of the heat source a temperature different from that at which"the 35 heat source is deactivated. This temperature difierence, ordifierence between the temperatures at which the heat source isactivated and deactivated, in itself causes the temperature of the spacebeing heated to depart from the desired value or degree of course; andfurther, all these expedients, so far as I am aware, involve regularlyor occasionally a materially greater terrai perature difference than isnecessary to avoid the annoyances of the simpler thermostaticarrangement mentioned above, and hence directly by reason of thetemperature difference regularly or occasionally cause the room or housetemperature to depart from the desired value or values to an unnecessaryextent. Still further, all commonly used heat sources, i. e. stokers,fur naces and radiators, lag more or less in responding to calls formore heat and less heat, the tent of the lag depending on previousperiods of activation or deactivation, and hence the prior expedientsused to reduce the annoyances of the Such thermostatic ele.

simpler thermostatic arrangements, in reducing the frequency of theheat-source-activating and deactivating cycles as compared with thesimplerthermostatic arrangement, compound the efiects of the lag in theheat source, with the result that 5 temperature of the space to beheated frequently overshoots and undershoots the desired temperature toan extent considerably greater than that represented by the temperaturedifference, and this effect is aggravated by the 10 regular oroccasional occurrence of a greater temperature difference than isnecessary.

In contrast to this, my invention involves a lesser temperaturedifference between the activation of the heat source and its more orless 15 complete deactivation, and a greater frequency of the activatingand deactivatingcycles. To this end 1 employ a thermostatic elementresponsive immediately to the temperature of the space being heated,generally speaking, and a time device, 20 as it were, to impose a delayof a certain period of "me or all successive changes the source. Thesedelays of mine, impos oniy between each activation and deactivation, arefor periods (at least averagir between say one-half or one minute andthe e requi ed for the heat source to raise the temperature o e spaceheated about two degrees Fahr. mposed only between deactivati ndactivatic-n, they are for periods (at least ave rig} between sayone-half or one minute and someth ng less than he time required thetemperature of the space to fall about two degrees Fahr.

r ther the matter, it is pointed "e prior commonly-used expedients toannoyances of the simple thermostatic ten; first mentioned thethermostatic 'len't is so constructed that once it has acted (e. abivnetallic element has warped) in a 49 manner to activate the heatsource, a change of temperature of some two degrees Fahr. is required tocause the thermostatic element to act reversely in a manner todeactivate the heat source. In contrast to this, my invention employs asbefore a thermostatic element subject to the temperature of the spacebeing heated, but in lieu of a thermostat construction requiring atemperature change to cause a reversal of the operations, it employs atime device, as it were, to in- 50 'terpose a delay of a certain periodof time between the movement of the thermostatic element to that extent(e. g. a certain bending of a bi-metallic element) which calls foractivation of the heat source and the actual activation of the heatsource. As compared with such prior systems, the delay imposed by mytime device is for between, say, one-half or one minute and somethingless than the time required for the heat source to raise the temperatureof the space about two degrees Fahr. Conversely of course, the timeddelay may be imposed on the other half of the cycle; in that case thedelay is for between say one-half or one minute and something less thanthe time taken for the temperature of the space being heated to fallabout two degrees Fahr. As a third alternative a delay can be imposed ineach half of each complete cycle.

The delays of successive cycles can be for equal periods, or for unequalperiods. As an example of the latter, the time device may operate torender the thermostatic element effective to activate or deactivate theheat source at periodic intervals. Where such a periodic time device isemployed to impose a delay on the activation of the heat source, thedeactivation being instantaneously under the control of the thermostat,the time device should function at a frequency between about twice perminute and about once per hour; on the other hand, where a periodic timedevice imposes its delays on only the other half of the cycle, i. e. onthe deactivation of the heat source, its frequency should be betweenabout twice per minute and about once every ten minutes. While fixedperiods of delay, and periodic operators of fixed periods, seem to besufficient, it is to be understood that my invention includes bothvariable periods and variable frequencies as well.

While the invention as thus broadly expressed can be embodied in variousforms, I believe preferable, as a specific form of my invention, thosearrangements or forms wherein action of the thermostatic element isrequired to cause activation or increased activation of the heat sourcefor sufficient time to materially change the state of the heat source onwhich the control system works. Also I believe preferable thosearrangements or forms of the broader invention wherein the delay isimposed during only one-half of each activatingand deactivating cycle,the initiation of the other half of each cycle following substantiallyinstantaneously after the movement of the thermostatic elementcorresponding to the arrival of the temperature at the thermostaticelement at some certain degree; this degree need not be constanthowever, but it may be variable; forexample, variable with the momentaryrate of temperature rise or fall at the thermostatic element. It ispreferable too, I believe, that the delay be imposed on the activation.Various embodiments of these specific forms of my invention areillustrated and described hereafter.

A further part of my invention has to do, primarily, with theelimination of the effect of the delay mechanism on the occurrence of anunusual or extraordinary condition. If, for example, the time device isarranged to impose a delay on the activating of the heat source, and thetemperature of the space being heated or to be heated is materiallybelow the temperature desired at the moment (say a matter of r two orthree or more degrees Fahr. below), this further part of my inventioncauses an immediate actuation of the heat source. Likewise, if a delayis imposed on the deactivation of the heat source, a similar expedientcan be employed to bring about an immediate deactivation of the heatsource on the rising of the temperature materially above the desireddegree. To this end I employ a thermostatic element arranged to changethe condition of the heat source (activate or deactivate it, as the casemay be) directly and substantially instantaneously after the need hasarisen. This thermostatic element can be a thermostatic element separateand distinct from the thermostatic element on the operations of whichthe delay is imposed, or it may be the same thermostatic element withadditional connections through which it can act by reason ofextraordinary movement resulting from the extraordinary condition. Theeffect can be transmitted to the heat source by requiring the timedevice or some part of it to assume the appropriate activating (ordeactivating) position immediately, or by action around the time device.

Also, certain specific forms of my invention wherein no relays are used,and which are better described with reference to certain figures of theaccompanying drawings, not only incorporate the foregoing matters of myinvention, but also incorporate in systems without relays the underlyingprinciple of an invention of one William M. Schweickart and for which anapplication for Letters Patent by him is being filed on an even dateherewith. By this further matter the heat source is operated in steps asit were. While the temperature of the space being heated stands below acertain degree, the heat source is operated at a certain high rate, forexample continuously; between this degree and some higher degree theheat source is operated at a lower rate, for example periodicallyactivated or deactivated; above the latter degree the heat source rateis further reduced, for example deactivated to a minimum degree. Insteadof there being only three steps, there may be more. This tends toreduce, particularly, overshooting due to lag in the heat source.

From the foregoing and the hereinafter described examples of myinvention as applied to temperature control, the application of myinvention to other conditions will be evident.

It will be understood that while hereinabove and hereafter I use thewords activate, deactivate and similar words with reference to the heatsource, my invention is not limited to complete cessation of heat supplyon deactivation, but, from a broader aspect, includes a bare change ofrate of heat supply. Also while the periods of delay are, for the mostpart, herein described as independent of temperature, it is to beunderstood that my invention includes modification of the time delayperiods, for example in accordance with the momentary temperature,temperature change rate, etc.

Other objects of the invention include the details and arrangement ofthe specific systems to be hereinafter shown and described and set forthin the appended claims.

Additional objects of the invention will become apparent as thedescription thereof proceeds.

For a more complete understanding of the invention, reference may be hadto the following description and accompanying drawings in which:

Fig. 1 is a schematic diagram showing one embodiment of the presentinvention,

Fig. 2 is a side view of the timing mechanism utilized in the system ofFig. 1,

Fig. 3 is an end view of the timing mechanism of Fig. 2,

Fig. 4 is a schematic wiring diagram showing tem of Fig. 1,

Fig. 5 is a schematic wiring diagram of a further modification ofthe'invention,

Fig. 6 is a schematic wiring diagram of a still further modification ofthe invention,

Fig. 7 is a side view of the timing mechanism utilized in the system ofFig. 6 and has certain parts in section,

Fig. 8 is a sectional view of the timing mechanism of Fig. 7 and istaken about on the line 6-6 of Fig. 7,

Fig. 9 is a schematic showing of a further modification of the inventionand showing how the relays of the previous figures may be dispensedwith,

Fig. 10 is a diagram showing a modified form of the system of Fig. 9,

Fig. 11 illustrates the manner in which a thermal timer may be utilizedin place of a mechanical timer in a system which operates similar to themanner in which the system of Fig. 9 operates, and

Fig. 12 is a schematic wiring diagram of a still further modification ofthe invention.

Referring first to Figs. '1, 2 and 3, a timer mechanism generallyindicated at 20 comprises amounting panel 2| to which is secured asuitably enclosed electric motor 22 which constantly drives a shaft 23at reduced speed by means of a gear reduction housed in casing 24. Thespeed of the motor 22 and the gear reduction housed in casing 24 arepreferably so arranged that the shaft 23 rotates at a speed explainedabove, that is to say at a speed generally less than about one rotationper half minute and something greater than one rotation in the timerequired for the room temperature to fall 2 Fahr., and preferably abouttwo to twelve rotations per hour. A disc 25 is secured to shaft 23 forrotation therewith and carries a crank pin 26 which isadapted, uponrotation of disc 25, to periodically engage the underside of a lever 21which is pivoted at 26 on mounting panel 2|. Upon raising of lever 21 bycrank pin 26, the lever 21 is brought. into engagement with a contact 29which is carried by a spring finger 36 herein shown as secured to thecasing 24 which encloses the reduction gear train. A coiled spring 3|has one of its ends secured to the outer free end of lever 21 and hasits other end secured to a pin 32 also shown as carried by the casing 24of the reduction gear train whereby-the coiled spring 3| biases thelever 21 in a direction to move the same from engagement with. thecontact 29. A stop pin 33, likewise shown as secured to the casing 24 ofthe reduction gear train, limits the movement of lever 21 under the biasof coiled spring 3|.

In the timing mechanism shown in Fig. 1, the lever 21 also carries ablock of insulating material 34 to which is secured a contact plate 35that is adapted to bridge contacts 36 and 31 when the lever 21 is inengagement with stop pin 33. The motor 22 of the timing mechanism isconstantly energized with the result that in the timing apparatusschematically shown in Fig. 1, the lever 21 is periodically raised bycrank pin 26 to disengage contact plate 35 from contacts 36 and 31 forrelatively short periods and to move lever 21 into engagement withcontact 29 for relatively short periods and is periodically returned tothe position shown by means of the coiled spring 3|.

The system of Fig. 1 illustrates a temperacontact 29.

ture control system for heating purposes and the temperature changingmeans is illustrated as a motor 36 which may be a stoker motor or anyother electrically operated device for raising the temperature of aspace or room to which a thermostat responds. The thermostat is shown ascomprising a bimetallic thermostatic element 39, a contact blade 40, anda cooperating contact 4| which preferably responds to a change ofcondition of the heat source, such as a room thermostat. Upon a fall inthe room temperature to which bimetallic element 39 responds, contactblade 49 moves into engagement with contact 4|. The system of Fig. 1further includes a relay comprising a relay coil 42 which, uponenergization, attracts an armature 43 that moves switch arms 44 and 45into engagement with contacts 46 and 41. Upon deenergization of relaycoil 42, armature 43 returns to the position shown in Fig. 1 whereinswitch arms 44 and 45 are disengaged from contacts 46 and 41respectively. High voltage electrical power is supplied by line wires 43and 49. Low voltage electrical power is supplied by the iow voltagesecondary 59 of a transformer 5| having a high voltage primary 52 whichis connected to line wires 46 and 49 by means of .wires 53 and 54.

In the operation of the system of Fig. 1, lever 21 is periodicallyraised into engagement with This engagement of lever 21 with contact 29in itself does not complete a circuit through relay coil 42. When thetemperature to which bimetallic element 39 responds falls to apredetermined value, contact blade 49 engages contact 4| but again nocircuit is completed through relay coil 42. However, when contact blade40 is in engagement with contact 4| and at the same time lever 21 israised into engagement with contact 29, then an energizing circuit forrelay coil 42 is established as follows: secondary 50, wire 55,bimetallic element 39, contact blade 49, contact 4|, wire 56, wire 51,lever 21, contact 29, wire 59, relay coil 42 and wire 59 to the otherside of secondary 59. Energization of relay coil 42 attracts armature 43as previously explained and moves switch arms 44 and 45 into engagementwith contacts 46 and 41. Engagement of switch arm 44 with contact 46establishes a holding circuit for relay coil 42 which is independent ofswitch arm 21 and contact 29 but is controlled by contact blade 49 andcontact 4|. This holding circuit is as follows: secondary 50, wire 55,bimetallic element 39, contact blade 49, contact 4|, wire 56, wire 60,contact 46, switch arm 44, wire 6|, relay coil 42 and wire 59 to theother side of secondary 53. Relay coil 42 will therefore remainenergized until such time as the temperature to which bimetallic element39 responds rises sufliciently to disengage contact blade 4|! fromcontact 4|. During the short period that lever 21 is in engagement withcontact 29, the system may possible operate with annoying frequency but.as soon as crank pin 26 has revolved sufficiently to allow switch arm21 to disengage contact 29, then all possibility of such annoying highfrequency operation will cease since the first time that contact blade40 thereafter disengages contact 4|, the relay coil 42 will bedeenergized and cannot again be subsequently energized until lever 21 isagain moved into engagement with contact 29.

When switch arm 45 has been moved into engagement with'contact 41, thenthe stoker motor 36 will be energized as soon as lever 21 returns to theposition shown in Fig. 1 wherein contact plate 35 bridges contacts 36and 31. This circuit is as follows: line 49, wire 62, contact 41,

switch arm 45, wire 63, contact 36, contact plate 35, contact 31, wire64, stoker motor 38, and wire 65 to line 48. It will be noted that thestoker motor 38 cannot be energized during that period when lever 21 isin engagement with contact 29 when there is a possibility of highfrequency operation of the thermostat, whereby current impulses will notbe transmitted to stoker motor 38. The relay coil 42 will remainenergized until contact blade 48 disengages contact 4| and during thistime stoker motor 38 will remain in continuous operation with theexception that the current supplied thereto will be momentarilyinterrupted whenever the crank pin 26 operates lever 21 to raise contactplate 35 out of bridging relation with contacts 36 and 31. In manyinstances, it will be found possible to entirely eliminate the switchcomprised by contact plate 35 and contacts 36 and 31. When contact blade48 finally disengages contact 4| to deenergize relay coil 42, theholding circuit therefor will additionally be broken by reason ofseparation of switch arm 44 from contact 46 with the result that relaycoil 42 cannot again be energized thereafter until lever 21 is againmoved into engagement with contact 29.

The system of Fig. 1 therefore provides an arrangement by means of whicha variable time delay is interposed between closing of the thermostatswitch (comprised by contact blade 48 and contact 4|) and energizationof stoker motor 38. The amount of the time delay depends upon theposition of crank arm 26 at the time contact blade 48 engages contact 4|and also depends upon the speed of rotation of disc 25. In this manner,a single circuit open contact bimetallic thermostat may be utilized witha minimum of high frequency operation without making too great asacrifice in the sensitivity of the thermostat since while a shortvariable delay is interposed between engagement of contact blade 48 withcontact 4| before the stoker motor 38 is energized, it will be notedthat immediately upon separation of contact blade 48 from contact 4|stoker motor 38 is deenergized. It will also be noted that this delaydoes not depend upon further temperature fall in the space to be heatedand is entirely independent thereof.

The switch 21-29 might be termed a starting switch which is operatedindependently of temperature changes whereas switch 48-4| is the.

holding switch controlled by temperature changes.

The system of Fig. 1 has been explained in connection with a heatTngsystem but it is apparent that this same system could be readilyutilized in connection with a cooling temperature control system or anyother desired type of control system. Likewise, while the delay has beenherein shown as interposed between a call for heat by the roomthermostat and the operation of the stoker motor, the delay couldequally well be interposed between opening of the thermostat circuit andstopping of the stoker motor as will hereinafter become apparent inconnection with other modifications of the invention.

Turning now to Fig. 4, the timer mechanism 28 is exactly the same asthat utilized'in Fig. 1 except that the supplemental motor switchcomprised by contact plate 35 and contacts 36 and 31 has not been shownalthough it will be understood that the same could be utilized in thesystem of Fig. 4 if desired. The parts of the timer mechanism 28 of thesystem of Fig. 4 have been referenced to correspond with the similarparts of the timer mechanism 28 of Figs. 1, 2 and 3.

The control system of Fig. 4 is again shown as a heating system oftemperature control and includes a space or room thermostat comprising abimetallic element 15 which, upon cooling, se-

quentially moves contact blades 16 and 11 respectively into engagementwith contacts 18 and 19. As is usual in such thermostats, contact blade11 engages contact 19 at a temperature substantially 2 lower than thatat which contact blade 16 engages contact 18 and, similarly upontemperature rise, contact blade 11 disengages contact 19 at atemperature about 2 lower than that at which contact blade 16 disengagescontact 18. The system of Fig. 4 includes a re lay comprising a relaycoil 88 which, upon energization, attracts an armature 8| that in turnmoves switch arms 82 and 83 into engagement with contacts 84 and 85respectively. The temperature changing means is again shown as anelectrically operated motor 86 which may control a stoker or any othersuitable temperature changing means. High voltage power is supplied byline wires 81 and 88 and low voltage power is supplied by the lowvoltage secondary 89 of a step-down transformer 98 having primary 9|which is connected to line wires 81 and 88 by wires 92 and 93.

When the temperature of the space or room falls sufficiently to causecontact blade 16 to engage contact 18, the relay coil 88 will beenergized the next time lever 21 is moved into engagement with contact29 by the following circuit provided contact blade 16 and contact 18 arestill engaged: secondary 89, wire 94, bimetallic element 15, contactblade 16, contact 18, wire 95, wire 96, lever 21, contact 29, wire 91,relay coil 88 and wire 98 to the other side of secondary 89. Armature 8|is thereupon attracted and moves switch arms 82 and 83 into engagementwith contacts 84 and 85 respectively. Engagement of switch arm 83 withcontact 85 energizes stoker motor 86 by the following circuit: line 88,wire 99, contact 85, switch arm 83, wire I88, stoker motor 86, and wire|8| to line 81. As hereinbefore stated, the supplemental motor switchoperated by lever 21 which is utilized in the system of Fig. 1 couldalso be used in the system of Fig. 4 and in case of such use, thissupplemental motor switch would be interposed in the wire I88.Engagement of switch arm 82 with contact 84 establishes a holdingcircuit for relay coil 88 which is independent of the switch comprisedby lever 21 and contact 29 and this holding circuit is as follows:secondary 89, wire 94, bimetallic element 15, contact blade 16, contact18, wire 95, Wire I82, contact 84, switch arm 82, wire I83, relay coil88 and wire 98 to the other side of secondary 89.

It will be noted that thus far the system of Fig. 4 corresponds exactlywith the system of Fig. 1 except for the omission of the supplementalmotor switch which may be used if desired. As pointed out in connectionwith Fig. 1, the stoker motor 86 of Fig. 4 will be operated anindefinite time interval after engagement of contact blade 16 withcontact 18. Where a relatively long timing period is used or if the roomtemperature should drop exceedingly quickly, it may happen that the roomtemperature will drop 2 below the desired point before lever 21 is movedinto engagement with contact 29. In such case, contact blade 11 willengage contact I9 before lever 21 is moved into engagement with contact29 and energize relay coil 80 independently of the switch comprised bylever 21 and contact 29. This circuit is as follows: secondary 39, wire94, bimetallic element I5, contact blade 11, contact I9, wire I04, relaycoil 80 and wire 98 to the other side of secondary 89. The stoker motor86 therefore can be operated independently of any time delay providedthe room temperature decreases sufliciently. Upon such energization ofrelay coil 80, switch arm 82 will be moved into engagement with contact84 whereupon the previously described holding circuit for relay coil 80will be established .with the result that operation of the stoker motor86 will be maintained after contact blade 11 disengages contact I9 anduntil contact blade I6 disengages contact I8 upon a rise in roomtemperature. The system of Fig. 4 therefore might be said to comprise atemperature control system in which a thermostat having a predetermineddifferential is utilized, together with means associated with thethermostat for operating the temperature changing means at least aportion of the time during which the room or space temperature isbetween the permissible maximum and minimum limits. Also the system ofFig. 4 might be described as a temperature control system in which thetemperature changing means is activated at least a portion of the timeduring which the temperature to be controlled is between certainpermissible limits, is activated continuously when the temperaturedeviates from one of the permissible limits in one direction and iscontinuously deactivated when the temperature deviates from the otherpermissible limit in the opposite direction. As applied to a heatingsystem, the system of Fig. 4 continuously operates means for increasingthe supply of heat when the temperature to be controlled falls below apredetermined minimum, is operated to supply no heat when thetemperature to be controlled reaches a predetermined maximum value andis operated at least a part of the time when the temperature to becontrolled is between the minimum and maximum limits.

Turning now to Fig. 5, a considerably different type of system isillustrated insofar mechani cal detailsand arrangement of parts is concealthough the system of Fig. 5 has operating acteristics which aresimilar to those found in the systems of Figs. 1 and 4. The system oflag. 5 is again shown as a heating system which includes a motor III!that may well represent any desired type of electrically operatedtemperature changing means such as a stoker motor and also includes aroom thermostat generally indicated at III. The room thermostat IIIincludes bimetallic actuator H2 which operates a blade .i'I3 thatcarries contact H4. The cooperating contact H5 instead of beingstationary (except possibly for purposes of manual adjustment) as isusual in construction of thermostats of this gen-- eral type is mountedupon an armature I I6 which is pivoted at In. A coiled spring H8 whichhas one of its ends secured to armature H6 and its other end secured toa stationary pin H9, biases armature H6 into engagement with a stop pinI20 whereby contact H5 is moved out of the normal range of movement ofcooperating contact H4. A magnetic pull coil I2I cooperates with.armature H6 and, when energized, is adapted to attract armature H6 andmove the same out oi engagement with stop pin I20 and bring contact I I5within the normal range of movement of contact H4. An adjustable stopscrew I22 limits the movement of armature I I6 when attracted by pullcoil I2I. Also associated with armature H6 is a magnetic holding coilI23 which, when energized, is adapted to maintain or hold armature H6 inits attracted position but is unable to move armature I I6 from theposition shown in Fig. 5 to its other position in which it engages stopscrew I22. The system of Fig. 5 also includes timing mechanism but inthis system the timing mechanism has been shown as a thermal timerinstead of a mechanical timer. This thermal timer comprises a bimetallicstrip I24, one end of which is secured and the other end of which isadapted, upon cooling of the bimetallic strip I24, to engage a contactI25. The timer further includes a heating element .I26 which, whenenergized, serves to heat bimetallic strip I24 and cause the free end ofthe same to move out of engagement with contact I25. Power is suppliedby wires I21 and I28.

With the parts in the position shown, the bimetallic strip I24 has beenheated sufiiciently to disengage contact I25 and is now cooling. As thebimetallic strip I24 continus to cool, its free end will engage contactI26 and establish a circuit as follows: line I2'I, wire I29, pull coilI2I, wire I30, contact I25, bimetallic strip I24, wire I3I, heatingelement I26 and wire I32 to line I28. Energization of heating coil I26again begins to heat bimetallic strip I24 to cause the free end thereofto move out of engagement with contact I25. Energization of pull coilI2I attracts armature H6 and moves the same into engagement with stopscrew I22 with the result that contact H5 is brought within the normalrange of movement of contact H4. If, at this time, the temperature ofthe room or space is below the desired value, Contacts H4 and H5 willbecome engaged. Such engagement of these contacts establishes energizingcircuits for stoker motor H and for hold coil I23. The energizingcircuit for hold coil I23 is as follows: line I28, wire H3, bimetallicelement H2, blade H3, contact H4, contact H5, armature H6, wire I34,hold coii I23, and wire I35 to line I21. The energizing circuit forstoker motor H0 is as follows: iine I28, wire I33, bimetallic elementH2, blade H3, contact H4, contact H5, armatur I I5, wire e136, stokermotor I I0 and wire I31 to 1 8 .firmature H8 will be retained or held iits attracted position by hold coil I23 irrespec strip 624 by heatingcoil to cool a... repeat the above cycle whereby t circuit tin ughheating coil 26 and pull coil is intermittently made and broken. Aspreviously pointed out however, anmature HE having once been moved toits attracted position by pull coil I iii will remain therein as long ashold coil I23 is energized, the energization of which in turn. isdependent upon engagement of cont c'ts H4 H5. Similarly stoker motor IIll w remain energized as long as contacts H4 and are in engagement.When the room or space temperature is restored to the desired valuebimetaliic element H2 will move Contact H4 out of engagement withcontact H whereupon stoker motor II ll and hold coil I23 will bedeenergized. If, at this time, pull coil I2I is also deenergizedarmature H6 will return to the position shown in Fig. 5.

It will therefore be seen that this system operates very similarly tothe manner in which the again be n system of Fig. 1 operates in that afall in the temperature of the room or space to be heated below thedesired value in itself is not sufficient to start operation of stokermotor III]. This fall in room temperature must be accompanied bymovement of contact H5 and this movement of contact II5 takes place avariable time interval after the room temperature has fallen below thedesired value. The contact I25 and bimetallic strip I24 comprise aswitch which might be termed a starting switch in that this switch mustbe closed to cause pull coil I 2| to attract armature II6 before theroom thermostat III is able to initiate stoker operation. In a similarmanner contacts I I4 and H5 might be said to comprise a holding switchin that upon engagement of these contacts the stoker motor IIO remainsenergized until contact II4 recedes from the position at which itengages contact H5.

In the system of Fig. 5 as in the other systems hereinbefore described,a single circuit room thermostat is utilized but a great deal of thepossibility of undesirable high frequency operation is eliminated whileretaining a large part of the thermostat sensitivity by the associationtherewith of a starting switch that is operated independently of changesin the temperature of the room or space to be controlled. Morespecifically, a variable time delay is interposed between a fall in theroom temperature below the desired value and initiation of stokeroperation.

Turning now to Figs. 6, 7 and 8, the system of Fig. 6 includes a timingmechanism which is shown in detail in Figs. 7 and 8. A base I40 supportsan electric motor MI by means of a suitable bracket I42. Motor I4Idrives a friction disc I 43 through a suitable gear reduction housed ina casing I44 so that the friction disc I43 is driven at a speed of notmore than about one revolution per half minute, and not less than onerevolution in less than the amount of time required to change thetemperature of the space being heated about two degrees Fahr. Thefriction disc I43 is abutted by a timing disc I45 which is mounted on ashaft I46 journaled in a bracket I41 and an end plate I52 which in turnare mounted upon basefi40. A coiled spring I48 abuts bracket I41 andtiming disc I45 to constantly bias the latter into engagement withfriction disc I43. An arcuate track I49 is mounted upon timing disc I45and concentric with the axis thereof, it being noted that the track I49does not form a complete circle. A lever I50 is pivoted on a pin I5Iwhich is carried by end plate I52 and this lever I50 is provided with adownward extension I53 which, with the parts in the position shown, liesin the path of and is abutted by the end I54 of track I49. Suchengagement of the end I54 of track I49 with projection I53 preventsrotation of timing disc I45 but the motor I4I, which is continuouslyenergized, is allowed to continue to rotate by reason of the slippingbetween friction disc I43 and timing disc I45. The extension I53 isprovided with a gateway I53a. An electromagnetic coil I55, whenenergized, is adapted to lift lever I50 and bring the gateway I53a ofextension I53 into registry with track I49 whereupon timing disc I45 isallowed to rotate in a counter-clockwise direction as viewed in Figs. 6and 8, as indicated by the arrows. Such movement of lever I 50 bringsthe same into engagement with a contact I56 which is carried by aflexible blade I5'I that is preferably secured to end plate I52. Thedisc I45 is provided with a pin 511 which will pass through gateway I53awhen lever I50 is in its lowermost position but which engages the lowerend of extension I 53 when the lever I50 is raised by electromagneticcoil I55.

Referring particularly to Fig. 6, the device I58 indicates anyelectrically controlled temperature changing device such as the stokermotor hereinbefore described in connection with Figs. 1, 4 and 5. Thesystem of Fig. 6 includes a room thermostat I59 which comprises abimetallic actuator I60 that controls a contact blade I6I which isadapted upon lowering of the temperature to which bimetallic element I60responds to engage a contact I62. Power is supplied by line wires I63and I64.

With the parts in the position shown in Fig. 6, the extension I53 is inthe path of and abutted by the end I54 of track I49 so that timing discI45 is stationary. The temperature of the room or space is above thedesired value and contact blade I6I of room thermostat I59 is out ofengagement with contact I62. Lever I50 is out of engagement with contactI56 so that the tem-' perature changing device I58 is deenergized and noheat or minimum heat is being supplied to the room or space to beheated. The temperature of the room or space will therefore lower andwhen a predetermined minimum temperature is reached contact blade I6Iwill move into engagement with contact I62 and energize electromagneticcoil I55 by the following circuit: line I64, wire I65, bimetallicactuator I60, contact blade I6I, contact I62, wire I66, electromagneticcoil I55, and wire I61 to line I63. Energization of electromagnetic coilI55 raises lever I50 into engagement with contact I56 and moves thegateway |53a of extension I53 into registry with track I49 whereupontiming disc I45 is released for rotation and begins to rotate in acounterclockwise direction. Engagement of lever I50 with contact I56energizes the temperature changing device I58 by a circuit as follows:line I64, wire I68, lever I50, contact I56, wire I69, temperaturechanging device I58 and wire I10 to line I63. The upper surface ofgateway I53a rides upon the upper surface of track I 49 and maintainslever I 50 in its elevated position so that even though contact bladeI6I of room thermostat I50 now leaves contact I62, the lever I50 will bemaintained in engagement with contact I56 to maintain temperaturechanging device I58 energized. If the room thermostat is still or againcalling for heat when disc I45 has substantially completed onerevolution, so that electromagnetic coil I 55 is energized, the lowerend of extension I53 will be engaged by the pin I45a and furtherrotation of disc I45 will cease. Disc I45 will thereafter remainstationary until the room thermostat becomes satisfied and deenergizeselectromagnetic coil I55 to release lever I50. When lever I50 isreleased, it will move to its lower position and gateway I 53a will moveinto registry with pin I45a whereupon disc I45 will return to itsinitial position wherein the extension I53 is abutted by track I49 andthe disc I45 is stationary. If, on the other hand, the electromagneticcoil I55 is deenergized when disc I 45 has substantially completed arevolution, lever I50 will immediately drop to bring gateway I53a intoregistry with pin I45a and the parts will return to their originalposition.

In the system of Fig. 6 therefore, immediately upon a call for heatresulting in engagement of contact blade I6I of room thermostat I59 withcontact I62 thereof, a circuit to the temperature changing device I 55will be completed and will thereafter be maintained completed until thetiming disc I has made substantially one complete revolution or cycle.The timing disc I45 is assured of making substantially one completerevolution even though the blade I5I substantially immediately separatesfrom contact I52. In this manner, a minimum firing period is insured andfurthermore there will always be a variable delay between opening of theroom thermostat and deenergization of the temperature changing device,this variable delay depending entirely upon the position of the end I1Iof track I49 in respect to the projection I53 of lever I50 at the timethe room thermostat opens the circuit to electromagnetic coil I55. Afterthe minimum firing period, the control is returned to the roomthermostat. The system of Fig. 6 therefore again demonstrates anothermanner in which a single circuit bimetallic open contact thermostaticswitch may be utilized with a minimum of high frequency operationwithout greatly sacrificing any of the sensitivity of the apparatus. Thesystem of Fig. 6 further demonstrates that the delay may be interposedbetween satisfying of the room thermostat and termination of operationof the temperature changing device instead of being interposed between acall for heat by the room thermostat and initiation of operation of thetemperature changing device, the latter operation having been shown inthe previously described systems.

Turning now to Fig. 9, at I15 is a household heating furnace, which isfired by a coal stoker of which the coal hopper I15, coal and airconveyor I11 leading therefrom to the furnace, blower I15 for providingthe combustion air, and electric motor I15 for driving the blower andfuel conveyor, will be recognized. As is apparent from this figure, themotor I15 illustrates specifically the motor of a furnace stoker; in abroader and more general sense, the motor I15 of this figure is alsorepresentative of any kind of power device operating in any way to varythe heat supplied by the furnace I15.

The temperature of the room or building heat ed by the furnace I19 iscontrolled by a thermostat I50 located therein or otherwise maderesponsive to the temperature of the room or building. At I5I isindicated the supply lines or source of electricpower for the motor I19.At I52 is illustrated the intermittently operating device which is hereshown as consisting of a cam disc I55, driven by an electric motor I54,and having a cam follower in theiorm of a hinged member I provided withan electrical contact I55 for engagement with the fixed electricalcontact I51. Contact I55 is shown Insulated from the cam follower I55,and contact I51 insulated from its carrying standard. A spring I55 willserve to hold the cam follower I05 in engagement with the edge of thecam disc I55. The cam disc I55, when rotating, is rotated at a rate ofthe order previously indicated, say of about one rotation in every tenminutes, and as illustrated serves-to hold the contacts I55 and I51 inengagement for about half of each rotation, and permits the two to standdisengaged for the other half of each rotation. One side of the supplyline "I is connected to one side of the motor I15. The other side of themotorv I15 is connected to the contact I55. Contact I51 is connected toa fixed contact I55 of the room thermostat I55. The bimetallic elementI50 of the thermostat is connected to the opposite side of thecurrentsource or supp y line III. The driving element for the intermittentlyoperating device I52, namely the electric motor I54, is connected inseries with the fixed contact I55 of the thermostat I50 across thesupply lines II. The bimetallic element of the thermostat I50 moves inthe direction of thearrow I as the temperature falls. It will beapparent therefore, that so long as the temperature of the thermostatI50 (or say the temperature of the space to be heated) is above thatdegree at which the bimetallic element engages the fixed contact I59,the intermittently operating device I52 remains inoperative, but whenthe temperature is below this degree (and the bimetallic element isengaged with contact I59) the intermittently operating device I52 closesthe motor switch I55 and I51 intermittently, thereby operating thestoker motor I19 intermittently (and hence coal and fuel are fed to thestoker intermittently), for periods of five minutes each, the motor I15(and coal and air feeds) remaining at rest during the interveningfive-minute periods. This intermittent operation may continue until thetemperature at the thermostat I50 rises again to the degree at which thebimetallic element will separate from the stationary contact I55. whenthis occurs, both the intermittently operating device I52 and the stokermotor I15 are deprived of current, and hence come to rest.

The stationary contact I59 is so related to the bimetallic element ofthe thermostat I50, that the two engage and disengage at approximatelythe temperature which it is desired to maintain in the house or roomcontaining the thermostat. A second stationary contact I5I of thethermostat is so placed as to be engaged by the bimetallic element at alittle lower temperature than the contact I59, say at a temperature twoor three degrees lower. This contact I5I, acting through conductor I52,short-circuits the intermittently engaging contacts I55 and I51,- whenengaged by the bimetallic element and hence serves to maintain thestoker motor I15 in continuous operation so long as the engagement atI5I con-'- tinues. Obviously therefore, the stoker is operatedcontinuously at the lowest temperatures; is

operated intermittently, say at five minute intervals, so long as thetemperature is approximately that desired at the thermostat I50; and isheld entirely inoperative when the temperature at the thermostat I50 isstill higher, and above that desired.

In order to avoid any tendency there may be for the thermostat tochatter, that is to say, to intermittently open and close its circuitsrapidly when the room thermostat is close to that degree which calls fora closing or opening, the thermostat may be provided with a permanentmagnet I55 acting, say, in a direction to hold the bimetallic element inengagement with the contacts I59 and I5I. The use of magnets for thispurpose is understood, and hence the foregoing mention of magnet I55will serve the present purposes.

Figure 10 is illustrative of the fact that the connection of theintermittently operating device to the thermostat in such a manner thatthe in termittently operating device is in operation only when thethermostat is calling for heat, is not an essential feature of a controlsystem. The room thermostat I 55 and the intermittently operating deviceI52 of this figure are exactly like the corresponding devices of Fig. 1,and bear corresponding reference' characters. be further describedtherefore. Also, the motor They need not I19 can be assumed (forillustrative purposes) to be the motor of a fumace-and-stokerarrangement such as is shown in Fig. 9. The motor I84 of theintermittently operating device I82 is permanently connected directlyacross the supply lines or source I8I in Fig. 10, and hence runscontinuously; however, the contacts I86 and I81 are connected in serieswith the thermostat I80 at the contact I89. Excepting for the fact thatthe motor I84 (and hence disc I83) are in continuous operation (ratherthan in operation only while the thermostat is calling for heat) theoperation is exactly like the operation of the arrangement of Fig. 9.

Devices and arrangements such as I have described, for example, can bemade a little more sensitive by, for example, biasing the roomthermostats in the opposite direction to the bias given by the permanentmagnet I93, or biasing in opposition to such a bias. This is illustratedby the electric heater I94 which appears in Fig. as an auxiliary. Thisheater serves to heat the thermostat I80 slightly, once the thermostatoperates to close the circuit at contact I89, and thereby cause thethermostat to open this circuit at a somewhat lower temperature than itwould do otherwise. As shown in this figure, the heating element I94 canbe connected in series with the contact I89, across the supply line I8I,so that the element is heated, and supplies heat to the bimetallicelement of the thermostat, as and when the circuit is closed at contactI89, but is entirely deprived of current while the circuit is broken atthis point. Such heating elements as auxiliaries to thermostats are wellknown and the foregoing description will suflice for the presentpurposes.

It is to be observed of course that this phase of my invention is notentirely limited to intermittently operating devices of the type shownat I82 in Figs. 9 and 10. Intermittent devices of quite other sorts maybe used instead. A single example embodying another form or type isshown in Fig. 11. The supply lines, or source of current I95 will berecognized, and the motor I96 represents aheat-controlling power devicelike, for example, the motor I19 of Figs. 9 and 10. As before, thethermostat I91 is provided with two stationary contacts I 98 and I99,and a permanent biasing magnet 200, similar in all respects to partsI80, I89, I9I and I93 of Figs. 9 and 10. The intermittently operatingdevice however, comprises a bimetallic (thermostat) element which, whencool, engages with the fixed contact 202, and which is provided with anelectric heater (e. g. a resistance wire) 203 which, when sufficientlyheated for a little time, causes the bimetallic element 20I to separatefrom the contact 202. The bimetallic element 20I, contact 202, andheater 203 are connected in series with the motor I96 and the contactI98 of the room thermostat I91, across the supply source I96. As before,the contact I99 of the room thermostat (which is engaged by thebimetallic element of the room thermostat at a somewhat lowertemperature than the contact I98) is connected in parallel with theintermittently operating device 20I, 202, 203 by the conductor 204. Theoperation of this device is obvious: So long as the temperature of theroom to be heated is above that degree at which contact I98 is engaged,no current is supplied to the motor I96, and the latter remainsinoperative. When the bimetallic element of the room thermostat engagescontact I98, current flows to and operates the motor I96, and alsopasses through the heating element 203; shortly thereafter the heatproduced by the heating element 203 causes the bimetallic element 20I toleave the contact 202, thus both stopping the motor I96 and deprivingthe heating element 203 of current; thereupon the heating element 203and nets like I93 and 200 of Figs. 9, 10 and 11, or any other mechanism,device or arrangement tending to reduce chattering at the roomthermostat, or to minimize the effect of such chattering, is entirely anessential to this phase of the invention. Nothing of the sort may benecessary under some circumstances. However, I contemplate that usuallysomething to minimize or eliminate such chattering, or the effect ofsuch chattering, will be desirable in these particular modifications.But when desirable, the effect is not necessarily obtained by biasing atthe room thermostat. Generally speaking, anything serving the purposemay be employed.-

Fig. 12, as in the case of the system of Fig. 6, illustrates anarrangement wherein the effect of chattering is eliminated by causing anadjustment of the heating device, once called for by the roomthermostat, to persist for at least a certain definite length of time;or to state the matter in another way, reverse adjustments called for bythe room thermostat are made subject to delay for intervals of timewhich may be entirely independent of any and all temperature changesoccurring at the room thermostat. These intervals of time are of theorder before indicated and such length that the thermostat will usuallyhave taken a definite position one way or the other, and either firmlyclosed or definitely opened its circuit or circuits. This result issecured by providing a circuit for keeping the intermittently operatingdevice in operation for say at least ten minutes, each time thethermostat calls for heat.

In Fig. 12, the room thermostat 2I0 with its fixed contacts 2 and 2I2corresponds in all respects to the room thermostat I80 with its contactsI89 and I9I respectively of Fig. 9 (the permanent magnet I93 of Fig. 9being omitted however). Likewise, the motor 2I3 can be regarded asdriving a stoker, exactly like the motor I19 in Fig. 9. Theintermittently operating device 2I4 has a cam disc 2I5, driving motor2I6 therefor, cam follower 2I1, contacts 2I8 and 2I9, and cam followerspring 220. In addition, the shaft carrying the cam disc 2I5 is alsoprovided with a second cam disc 22I entirely circular except for asingle narrow notch 222. For this cam disc 22I a hinged cam follower 223is provided, having a spring 224 to keep it in engagement with the camdisc HI, and provided with a contact 225 for engagement with the fixedcontact 226; the arrangement is such that contact 225 engages 228,except when the notch 222 stands opposite the cam follower 223. Thesource of current, as before, is at 221. It will be observed that theoperating motor 2 is connected in series with the contacts 2|! and 2l9across. the suppiy'line 221. Likewise, the driving element or motor 2"of the intermittently operating device 2 II, is connected in series withthe (higher temperature) contact 2| 2 of the room thermostat, across thesupply line 221. Figure 12 illustrates the room thermostatandintermittently operating device in the positions they have when thetemperature of the room is above the desired degree. It will be observedthat the circuit through operating motor 2 I 3, and also the circuitthrough the motor -2l8 of the intermittently operating device, are

both open, and hence both of these motors are .at rest.

As the temperature of the room falls and the room thermostat closes itscircuit at contact 2 l2, the motor 2l6 of the intermittently operatingdevice begins to rotate; as it begins to rotate, cam follower 223 isthrust out of the notch 222 in cm disc 22l, and thereby contact 225 isengaged with contact 226. It will be observed that this closes a circuitthrough the motor 2|6 of the intermittently operating device, across thesupply line 221, quite independent of the thermostat contact 2|2.Regardless therefore of whether or not the engagement at contact 212 isbroken immediately after it is made (i. e. by chattering at thethermostat) the intermittently operating device must continue inoperation for at least one complete revolution; at the end of thisrevolution, cam follower 223 will drop into notch 222 and open theholding circuit at 225-226; during this rotation, contact 2 has engagedcontact 2l9 for say, five minutes, and hence the operatingmotor 2I3 hasbeen activated for five minutes to raise the temperature to which theroom thermostat 2I0 responds. If this has served to raise thetemperature to which'room thermostat 2Il| responds, sufliciently todefinitely open the circuit at M2, the intermittently operating devicenow stops, but otherwise continues to make at least one more completerotation of its cam disc. In other words, the intermittently operatingdevice always operates for one or more intervals of ten minutes each(assuming the speed of rotation is one rotation per ten minutes) but themotor 2" is energized only a portion of this time whereas in the systemof Fig. 6, the'device I58 is energized during a complete revolution ofthe timing disc 5. If the temperature falls to the point ,where thecircuit is closed at contact 2| I,

' the motor 2I3 is put into continuous operation as before, and as willbe apparent from the drawings.

It will be readily appreciated that many changes and modifications canbe made to the system heralnbefore disclosed without departing from theinventions therein set out and I intend, therefore, to be limited onlyin the perview of the appended claims.

I claim as my invention:

1. In an automatic fuel supply control system, a room thermostat, fuelsupply means, constantly operating timing means, means associated withthe room thermostat and timing means for controlling the operation ofthe fuel supply means including a relay circuit having therein a pair 7of room thermostat contacts and a second pair of contacts lmder-thecontrol of said timing means and opened and closed thereby several timesa day, a second pair of room thermostat contacts closed at a diflerenttemperature than said first pair, and a second relay circuit controlledby said second pair r contacts.

2. In a control system, a main control having first and second pairs ofcooperating contacts, electromagnetic means, a continuously operatingtimer, a second pair of contacts opened and closed by the timer severaltimes a day, an energizing circuit for the electromagnetic meansincluding one pair of said main control contacts andsaid timer contacts,and control means associated with and operated by said electromagneticmeans, a second circuit for said electromagnetic means controlled by theother pair of said main control contacts.

3. In a control system, a single circuit switch responsive to acondition, a starting switch operated independently of the condition towhich the first mentioned switch responds, a device'to be controlled, astarting circuit in control of said device including said single circuitswitch and said starting switch in series, a holding switchautomatically movable to closed position upon energization of thestarting circuit, and a holding circuit including said holding switchand operative to control the device to be controlled independently ofsaid starting circuit, said single circuit switch and said holdingswitch being connected in series in said holding circuit.

4. In a temperature control system, a room thermostat, a switchhaving acontact moved by said room thermostat, a temperature changing device, astarting circuit including said thermostat contact in control of thetemperature changing device, a holding switch closed upon energizationof the starting circuit, a holding circuit including the holding switchfor maintaining said temperature changing device in operation, a thirdswitch connected in the starting circuit in series.

with the thermostat switch but located outside the holding circuit, andmeans for periodically opening and closing said third switch independ-Ill ently of the room thermostat switch, said thermostat switch beinginoperative to set up the holding circuit when said third switch isopen.

5. In a control system, a highly sensitive and relatively delicate maincontrol including a pair of contacts and responsive to a condition whichit is desired to control, a second pair of contacts operated by meansother than the condition it is desired to control, a relay, a holdingswitch operated thereby, an initial energizing circuit for said relaycontrolled only by said two pairs of contacts in series, a holdingcircuit for said relay controlled only by said pair of main controlcontacts and said holding switch, and a device for changing saidcondition controlled by the relay.

6. In a control system, a highly sensitive and relatively delicate maincontrol including a pair of contacts and responsive to a condition whichit is desired to control, a timer, a second pair of contacts operated bythe timer, a relay, a holding switch operated thereby, an initialenergizing circuit for said relay controlled only by said two pairs ofcontacts in series, a holding circuit for said relay controlled only bysaid pair of main control contacts and said holding switch, and a devicefor changing said condition controlled by the relay.

'1. In a temperature control system, a highly sensitive and relativelydelicate thermostat including a pair of main control contacts, a timer,a second pair of contacts operated by the timer,

a ,relay, a holding switch operated thereby, an

ing switch, and a temperature changing device controlled by the relay.

8. In a temperature changing system, in combination, temperaturechanging means, electromagnetic means in control thereof, a holdingswitch moved to closed position by said electromagnetic means uponenergization thereof, a temperature responsive actuator, .a singlecircuit switch controlled thereby, timing means, a timer controlledswitch, an initial energizing circuit for said electromagnetic meanscontrolled by said second named switch and timer switch in series, and aholding circuit for said electromagnetic means controlled by said secondnamed switch and holding switch in series, said holding circuit beingindependent of said timer switch.

9. A control system, comprising, a single circuit main control switch,electromagnetic means, two switches moved to closed position therebywhen energized, a timer, a first timer switch periodically closedthereby for periods of relatively short duration, a second timer switchmoved to open position while said first timer switch is closed, aninitial energizing circuit for said electromagnetic means controlled bysaid main control switch and first timer switch in series, a holdingcircuit for the electromagnetic means controlled by the main controlswitch and one of said electromagnetically operated switches in seriesand independent of said timer switches, electrical heat changing means,and a circuit therefor controlled by said second timer switch and theother of the electromagnetically operated switches.

10. In a temperature control system, a sourcev of heat'for the space tobe heated, an element, movable by change of condition of said heatsource and responsive substantially immediately to conditions at itself,to change the rate of heat production by said source, a time devicewhich substantially periodically and at a frequency of between abouttwice per minute and less than once per hour renders said elementmomentarily efiective to change the condition of said heat source in onedirection and means to permit said element to maintain said change inone direction and to bring about a change of the condition of the heatsource in the reverse direction substantially immediately uponappropriate movement of said element at any time.

11. In a temperature control system, a source of heat for the space tobe heated, an element, movable by change of condition of said heatsource and responsive substantially immediately to conditions at itself,to change the rate of heat production by said source, a time devicewhich substantially periodically and at a frequency of between abouttwice per minute and less than once per hour renders said elementmomentarily effective to activate said heat source, and means to permitsaid element to maintain said heat source in activated condition and todeactivate the heat source substantially immediately on movement of saidelement to a deactivating position at any time.

12. In a heating installation, a source of heat 13. In a heatinginstallation, a source of heat for the space to be heated, and a controlsystem therefor including a holding circuit to maintain a change ofcondition of said heat source, a starting circuit to initiate a changeof condition or said heat source when said holding circuit is in acondition to maintain said change, a thermostatic element responsive tothe condition of said heat source to cause said holding circuit to ceasemaintaining said change of condition, and a time device operative onsaid starting circuit at intervals greater than one-half minute and lessthan one hour.

14. In a control system, a main control having a pair of cooperatingcontacts, electromagnetic means, a continuously operating timer, asecond pair of contacts continuously opened and closed by the timerseveral times a day, an energizing circuit for the electromagnetic meansincluding said main control contacts and said timer-operated contacts,control means associated with and operated by said electromagneticmeans, and a holding circuit for said electromagnetic means controlledby said main control and independent of said timer-operated contacts.

15. In a control system, a pair of switches responsive to changes in a.condition which are sequentially closed upon a change in said conditionin one direction, a starting switch operated independently of thecondition to which said first mentioned switches respond, a device to becontrolled, a first starting circuit in control or said device includingsaid starting switch and the first to close of said first-mentioned twoswitches, and a second starting circuit for said device controlled bythe second to close of said first-mentioned switches.

16. In a control system, a pair of switches responsive to changes in acondition which are sequentially closed upon a change in said con--dition in one direction, a starting switch, means to periodically closesaid starting switch, a device to be controlled, a first startingcircuit in control of said device including said starting switch and thefirst to close of said condition responsive switches, a holding switchautomatically movable to closed position upon completion of said firststarting circuit, a holding circuit in control of said device, includingsaid holding switch and the first to close of said condition responsiveswitches, and a second starting circuit in control of said devicecontrolled by the last to close of said condition responsive switches.

GORDON M. PELTZ.

